Mepolizumab add-on after relapse during rituximab maintenance in myeloperoxidase-antineutrophil cytoplasmic antibodies-positive eosinophilic granulomatosis with polyangiitis: A case report and literature review.

Eosinophilic granulomatosis with polyangiitis is a heterogeneous vasculitic and eosinophilic disorder in which patients who are positive for myeloperoxidase-antineutrophil cytoplasmic antibody (MPO-ANCA) often develop glomerulonephritis and peripheral neuropathy and may require prolonged immunosuppressive therapy. Although rituximab (RTX) and mepolizumab have been used in selected patients with eosinophilic granulomatosis with polyangiitis, relapse during RTX maintenance remains difficult to manage. We report the case of a 59-year-old woman with adult-onset asthma and chronic rhinosinusitis who presented with severe eosinophilia, mononeuritis multiplex, MPO-ANCA positivity, and pauci-immune necrotising glomerulonephritis. Induction therapy with high-dose glucocorticoids, intravenous immunoglobulin, and RTX achieved clinical remission and allowed the tapering to a low dose of prednisolone. Despite RTX maintenance, she later relapsed with recurrent sinonasal symptoms, worsening neuropathic complaints, and a marked rise in MPO-ANCA levels. In this setting, a further escalation of immunosuppression during maintenance, including cyclophosphamide, may be considered; however, given the possibility that residual eosinophilic inflammation contributed to ongoing disease activity, including autoantibody production, mepolizumab was added after retreatment with RTX as sequential therapy. Symptoms stabilised and improved over the subsequent months, MPO-ANCA titres progressively declined to the normal range, and prednisolone was discontinued. Remission has been maintained on mepolizumab without further RTX maintenance. This case suggests that sequential eosinophil-targeted therapy may help consolidate remission after a relapse during RTX maintenance in MPO-ANCA-positive eosinophilic granulomatosis with polyangiitis.